Electric and hybrid vehicles typically include alternating current (AC) electric motor(s) that are driven by a direct current (DC) power source, such as a high voltage battery pack. The battery pack provides direct current to inverter module(s), which perform a rapid switching function to convert the DC power to AC power which drives the AC electric motor(s).
The AC electric motors typically include a rotor and stator assembly. Proper control of the AC electric motors depends upon a number of parameters including the temperature of the rotor and stator during operation. When the AC electric motors are “started” (that is, turned on, commonly referred to as “Key On”), it is common to initially estimate the rotor temperature as being approximately equal to the stator temperature. Normally, this initial rotor temperature estimate works well and rotor temperature tracking or estimation circuitry can then accurately track temperature changes in the rotor during operation. However, in the event the AC electric motors are turned off (commonly referred to as “Key Down”) and then quickly back on (commonly referred to as a “hot start”), the rotor temperate could be as much as 80° C. above the stator temperature. Accordingly, estimating the rotor temperature to be about that of the stator could lead to overheating if full torque is applied to the electric motor, since typical rotor temperature estimation circuits respond at a slow rate of change.
Accordingly, it is desirable to provide a simple, reliable and cost effective solution to rotor temperature estimation following “hot starts” in electric or hybrid electric vehicles. Additionally, other desirable features and characteristics of the present invention will become apparent from the subsequent description taken in conjunction with the accompanying drawings and the foregoing technical field and background.